Examples of electric vehicles, where left and right traveling units are driven via left and right motors, respectively, include electric truck vehicles and various working machines, such as snow removing machines and cultivators. Particularly, the working machines tend to prove more useful if they are capable of turning left and right with smaller turning radii depending on the working states.
To achieve a reduced turning radius of an electric vehicle, there are generally employed two approaches: (1) a “pivot turn” approach that causes the electric vehicle to make a U-turn by forward-rotating the outer traveling unit (i.e., one of the two traveling units which is located inward of the other as viewed in the turning direction) with the inner traveling unit placed in a stopped (deactivated) state; (2) a “spot turn” approach that causes the electric vehicle to make a U-turn by reverse-rotating the inner traveling unit while forward-rotating the outer traveling unit.
The “spot turn” is more preferable to enhance the turning capability of electric vehicles, and one example of such electric vehicles is proposed in Japanese Patent Application Laid-open Publication No. 2002-137755 and will be discussed below with reference to FIGS. 13A and 13B.
The electric vehicle 200 shown in FIG. 13A includes left and right electric motors 203L and 203R that are powered by a battery 202, accommodated in a space defined by a vehicle body frame 201, to rotate left and right driving wheels 205L and 205R via driven shafts 204L and 204R. Left and right crawlers 206L and 206R are driven via the left and right driving wheels 205L and 205R. Truck box 210 is placed on the vehicle body frame 201, and a control or operation panel 211 and control unit 212 are provided behind the truck box 210. On the operation panel 211, there are provided a single accelerator lever (speed adjusting lever) 213, left and right brake levers 214L and 214R, and left and right turning switches 215L and 215R.
The control unit 212 collectively controls the left and right motors 203L and 203R and left and right brakes 207L and 207R on the basis of respective detected operating positions of the accelerator lever 213 and brake levers 214L and 214R.
The accelerator lever 213 is an operation lever operable by the human operator to instruct forward movement, stoppage or rearward movement of the left and right crawlers 206L and 206R and to continuously switch from low-speed forward/ rearward travel to high-speed forward/rearward travel of the vehicle via the left and right crawlers 206L and 206R. Operating position of the accelerator lever 213 can be monitored via a not-shown accelerator potentiometer (that functions as a speed adjustment means).
While walking behind the electric vehicle with both hands holding left and right operating handles 221L and 221R extending rearward from rear portions of the vehicle body frame 201, the human operator can not only cause the electric vehicle to travel forward/rearward, turn or stop by operating any of the accelerator lever 213, brake levers 214L, 214R, etc. on the operation panel 211, but also cause the electric vehicle to make a spot turn by operating the left or right turning switch 215L or 215R,.
By the human operator depressing the right turning switch 215R as depicted by arrow Pu in FIG. 13B, the left motor 203R is rotated in the forward direction to drive the left crawler 206L in the forward direction, and simultaneously the right motor 203R is rotated in the reverse direction to drive the right crawler 206R in the rearward direction. Consequently, the electric vehicle 200 can make a right spot turn about a turning center G (i.e., a center point, in front-and-rear and left-and-right directions, between the left and right crawlers 206L and 206R) with a turning radius R corresponding to a distance to a left corner of the truck box 210.
To cause the electric vehicle 200 to travel forward or rearward, the human operator manipulates the operating handles 221L, 221R etc. with one hand while adjusting the vehicle speed by holding and manipulating the accelerator lever 213 with the other hand.
Also, to cause the electric vehicle 200 to make a spot turn under such operating conditions, the human operator temporarily lets go of (i.e., takes the hand off) the accelerator lever 213 and operates the left or right turning switch 215L or 215R. However, each time a spot turn is to be made, it requires certain skill for the human operator to temporarily let go of the accelerator lever 213 and operate the left or right turning switch 215L, 215R located at a considerable distance from the various levers. Therefore, further improvements have to be made in order to enhance the operability or usability of the conventional electric vehicle 200, especially, for an enhanced spot-turning capability of the vehicle.